The present invention relates to a drain trap to be laid underground for discharging water within the ground.
Hitherto drain pipes provided with a number of water gathering apertures distributed over the peripheral surfaces of said pipes have been used as drain traps. However, such drain pipes have the disadvantage that sand and earth, etc. are often apt to enter said water gathering apertures distributed on the peripheral surfaces of drain pipes together with subterranean water, so that the ground under which the drain pipes are buried, suffers serious erosion through said drain pipes over a period of years to form cavities around the buried drain pipes, such formation of cavities causing subsidence of ground surfaces or landslide. Moreover, dependent on the way in which water gathering apertures are formed, that is, the shape or the size thereof, apertures may be clogged so that the rate of drainage decreases and, furthermore, the boundary for gathering water under the ground through said water gathering apertures may also be decreased.